JPH06324682A - Piezoelectric buzzer driving device - Google Patents

Abstract

PURPOSE:To obtain the piezoelectric buzzer driving device which eliminates a waste of a current and generates a buzzer sound with an excellent timbre. CONSTITUTION:A transistor(TR) 11 and a TR 13 are turned ON to supply a current to an inductor 12. Then when the TR 13 is turned OFF, a counter electromotive force is generated at the inductor 12. This counter electromotive force is applied to a piezoelectric buzzer 15 through a diode 14 and held. Then a TR 16 is turned ON to discharge the voltage held in the piezoelectric buzzer 15. This operation is repeated at specific timing to make the piezoelectric buzzer 15 vibrate, thereby generating the buzzer sound.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric buzzer driving device which needs to produce a large and stable sound at a low power supply voltage.

[0002]

2. Description of the Related Art As a conventional piezoelectric buzzer driving device, a device that drives a piezoelectric buzzer by a counter electromotive force of an inductor is known. Such a device is, for example, as shown in FIG. 4, a power supply 1 and an inductor 2 having one end connected to the positive electrode of the power supply 1.
And a transistor 3 connected to the other end of this inductor 2.
And a piezoelectric buzzer 4 connected in parallel to the inductor 2. The base of the transistor 3 is connected to an input terminal 5 to which a control signal from a control device (not shown) is input via a base resistor, and the emitter is grounded.

The signals of the respective parts of the piezoelectric buzzer driving device thus constructed will be described with reference to FIG. 5A is a control signal applied to the input terminal 5, FIG. 5B is a collector current of the transistor 3, and FIG.
Indicates the back electromotive force generated in the inductor 2, respectively. First, the control device (not shown) is connected to the input terminal 5 as shown in FIG.
A control signal (pulse signal) as shown in (a) is input. When this control signal is at "H" level, the transistor 3 is turned on, and the current from the power source 1 is
As shown in (b), the current gradually increases until it is saturated in the inductor 2. Then, after the current is saturated, when the control signal becomes “L” level, the transistor 3 is turned off and the current flow in the inductor 2 is cut off. At this moment, the inductor 2 is moved by electromagnetic induction as shown in FIG.
A back electromotive force having a high voltage which is 3 to 4 times as high as that of the control signal is generated. Then, this counter electromotive force is generated by the piezoelectric buzzer 4.
Applied to. Then, since the counter electromotive force vibrates and is attenuated and converges to the reference potential, the piezoelectric buzzer 4 also vibrates according to the damped oscillation of the counter electromotive force, and a buzzer sound is generated.

[0004]

However, the above-mentioned prior art has the following problems. That is, when the time constant of the inductor 2 is smaller than the frequency of the control signal, the current flowing through the inductor 2 is saturated immediately. The current after the saturation does not contribute to the generation of the counter electromotive force in the inductor 2 and is simply consumed as heat in the inductor 2, so that the consumed current becomes large and the current is wasted. On the contrary, if the time constant of the inductor 2 is made larger than the frequency of the control signal in order to reduce the consumption current, it becomes difficult for the current to flow in the inductor 2. Therefore, the current flow in the inductor 2 is interrupted before the current sufficiently flows in the inductor 2 (before saturation). As a result, the counter electromotive force generated in the inductor 2 also decreases, and the buzzer sound of the piezoelectric buzzer 4 also decreases. In this way, the buzzer sound of the piezoelectric buzzer 4 depends on the time constant of the inductor 2 and the frequency of the control signal, and therefore the circuit designer must select the optimum value to obtain the desired buzzer sound. , Circuit design became difficult. In addition, since the counter electromotive force generated in the inductor 2 has a ringing waveform that attenuates and vibrates, the vibration of the piezoelectric buzzer 4 also corresponds to this ringing waveform, and the buzzer sound is an offensive tone with many harmonic components. .

The present invention has been made in view of the above-mentioned problems, and an object thereof is to obtain a piezoelectric buzzer driving device which eliminates waste of current and generates a buzzer sound with a good tone color.

[0006]

In order to achieve the above object, in the piezoelectric buzzer driving device of the present invention, a power source,
An inductor for generating a back electromotive force connected to the power source; a first switching means for controlling a time for which a current is passed from the power source to the inductor to generate a back electromotive force; and the inductor. Applied to the piezoelectric buzzer, a piezoelectric buzzer connected to one end of the piezoelectric buzzer, a backflow prevention unit disposed between the piezoelectric buzzer and the inductor, for applying a back electromotive force generated in the inductor only in the piezoelectric buzzer direction. A second switching unit for discharging the voltage held by the backflow prevention unit after a predetermined time, and a control unit for controlling ON / OFF of the first switching unit and the second switching unit. Characterize.

[0007]

In the piezoelectric buzzer drive device configured as described above, the time for flowing the current through the inductor is optimized by the first switching means, and the peak value of the counter electromotive force generated in the inductor is controlled by the backflow prevention means. , And then discharged by the second switching means at a predetermined timing. By repeating the operation of holding / discharging the counter electromotive force in this piezoelectric buzzer, the piezoelectric buzzer vibrates and a buzzer sound is generated.

[0008]

Embodiments of the piezoelectric buzzer driving device of the present invention will be described below with reference to FIGS. FIG. 1 shows a circuit diagram of a piezoelectric buzzer driving device of the present invention. A power source 10 including a battery or the like has its negative electrode side grounded and its positive electrode side connected to an emitter of a PNP type transistor 11. The collector of the transistor 11 is connected to one end of an inductor 12, which is a counter electromotive force generating means, the other end of the inductor 12 is connected to the collector of an NPN type transistor 13, and the emitter of the transistor 13 is grounded. There is. And this transistor 11 and transistor 1
The first switching means is constituted by 3. In addition, a diode 14 as a backflow preventing means and a piezoelectric buzzer 15 are connected in parallel with the transistor 13. In addition,
The anode side of the diode 14 is connected to the collector of the transistor 13, the cathode side of the diode 14 is connected to the piezoelectric buzzer 15, and the other end of the piezoelectric buzzer 15 is grounded. The collector of an NPN transistor 16 which is the second switching means is connected between the diode 14 and the piezoelectric buzzer 15, and the emitter of the transistor 16 is grounded. The base of the transistor 11 is via the base resistor 17, the clamp circuit 18, and the conduction time varying means 19, and the base of the transistor 13 is the base resistor 20, the inverter 21, and the clamp circuit 1.
8. The base of the transistor 16 is connected to the input terminal 23 via the capacitance variable circuit 19 and the base resistor 22, respectively. The capacitance variable circuit 1
9 is a first capacitor 19a and this first capacitor 19a
a second capacitor 19b arranged in parallel with a and a second capacitor 19b
It is composed of an analog switch 19c as a second capacitor connecting / disconnecting means for controlling connection / disconnection of the capacitor 19b, and the electrostatic capacitance variable circuit 19 and the base resistor 17 constitute a differentiating circuit. Function. Then, this differentiating circuit is the capacitance variable circuit 1
By changing the time constant of the differentiating circuit by turning on / off the analog switch 19c of No. 9, it becomes possible to change the on / off timing of the transistor 13. The clamp circuit 18 is composed of two Schottky diodes 18a and 18b, and the capacitance variable circuit 1
The voltage in the positive direction exceeding the power supply voltage generated at the output of 9 is prevented to protect the inverter 21.

Next, the operation of the piezoelectric buzzer driving device shown in FIG. 1 will be described with reference to the waveform diagram of FIG. In this example, the analog switch 19 is turned on so that a sufficient current flows through the inductor 11, and the capacitance variable circuit 1
The operation when the time constant 9 is increased will be described. 2A is a waveform diagram of the control signal input to the input terminal 23 (point A in FIG. 1), and FIG. 2B is a waveform diagram of the control signal after passing through the capacitance variable circuit 19. (B in FIG. 1
2), and an output waveform diagram of the inverter 21 (see FIG. 1).
2C is a waveform diagram of the voltage appearing at the collector of the transistor 13 (point D in FIG. 1), and FIG. 2E is a waveform diagram of the drive voltage applied to the piezoelectric buzzer 15 (see FIG. 1). E point)
Is. Each component of the piezoelectric buzzer driving device has a power source 10
Is 5 V, the inductor 12 is 560 μH, the base resistor 17 is 1 kΩ, and the first capacitor 19a is 2200 p.
The F and second capacitors 19b are of 0.03 μF. The vertical axis of FIG. 2 indicates the voltage (FIGS. 2 (a), (b),
One scale on the vertical axis of (c) is 1 V, and FIGS.
Of 1 represents 5 V), and the horizontal axis represents time (1 scale represents 0.1 ms).

First, a control signal (pulse signal) having a basic frequency of 2 kHz as shown in FIG. 2A is input to the input terminal 23 from a control device (not shown) (usually a microcomputer). When this control signal is at "H" level, the transistors 11 and 1
Since 3 is off and no current flows in the inductor 12, no counter electromotive force is generated, and since the transistor 16 is on, no voltage is held in the piezoelectric buzzer 15. . Next, when the control signal changes from the “H” level to the “L” level, the “L” level voltage is again applied to the base of the transistor 11 and the transistor 1 again.
The base of No. 3 is inverted by the inverter 21 and the voltage of "H" level is applied to each, the transistors 11 and 13 are turned on, and the power source 10 is supplied to the inductor 12.
Current flows from. Note that the base of the transistor 16 has a voltage of "L" level and is turned off. Then, as shown in FIG. 2B, the first and second capacitors 19a and 19b of the capacitance variable circuit 19 are driven by the current from the power source 10 flowing from the emitter of the transistor 11 through the base of the power source 10. It is gradually charged to a voltage (about 4.4 V) obtained by subtracting the base-emitter potential Vbe (0.6 V) of the transistor 11 from the voltage (5 V).
When the voltage of the first and second capacitors 19a and 19b exceeds the threshold value of the inverter 21 (2.5V which is half of the power supply voltage in this example), the output of the inverter 21 becomes "
The transistor 13 is turned off, and the transistor 13 is turned off. The time during which the transistor 13 is on, that is, the energization time of the inductor 12 depends on the time constant of the differentiating circuit. Inductor 12
The time constant (values of the base resistor 17 and the first and second capacitors 19a and 19b) of the differentiating circuit adapted to the inductor 12 is set so that the energizing time is such that the current flowing through the circuit is almost saturated. Then, when the transistor 13 is turned off, the current flow of the inductor 12 is suddenly cut off, so that the peak value of the inductor 12 is 5 times the voltage of the power source 10 (see FIG. 2D). A back electromotive force of about 25 V) is generated. The counter electromotive force is rectified by the diode 14 and applied to the piezoelectric buzzer 15. At this time, the transistor 16 is in the off state, and the backflow prevention diode 14 is provided between the inductor 12 and the piezoelectric buzzer 15. Therefore, the piezoelectric buzzer 15 and the diode 14 function as a so-called peak hold circuit. As shown in FIG. 2 (e), the inductor 1 is attached to the piezoelectric buzzer 15.
The peak value of the back electromotive force generated in 2 is retained. next,
When the control signal becomes "H" level again, the transistor 1
At the same time that 1 is turned off, the transistor 16 is turned on, the voltage held in the piezoelectric buzzer 15 is discharged, and the voltage across the piezoelectric buzzer 15 becomes 0V. Then, by repeating the operation of applying / holding the counter electromotive force to the piezoelectric buzzer 15 and discharging as described above, the piezoelectric buzzer 1
5 vibrates according to the cycle of its operation. In the case of this embodiment, a duty ratio of about 40 as shown in FIG.
%, Vibration according to the pulse waveform of frequency 2 kHz,
This is the buzzer sound. Since the piezoelectric buzzer vibrates more and generates a larger buzzer sound as the difference in applied voltage is larger, the voltage applied to the piezoelectric buzzer 15 is about 5 times the power supply voltage (as in the present embodiment). About 25V), a sufficiently large buzzer sound can be obtained.

Next, a method of switching the volume of the piezoelectric buzzer 15 in this embodiment will be described with reference to FIG.
The waveform charts of FIGS. 3A to 3E are shown in FIG.
Corresponding to the waveform diagrams of (a) to (e), the scale is also the same unit. The switching of the volume of the piezoelectric buzzer 15 is performed by reducing the time constant of the differentiating circuit described above. Specifically, this is performed by turning off the analog switch 19c of the capacitance variable circuit 19 and disconnecting the second capacitor 19b from the circuit. The operation at this time will be described. First, the analog switch 19c is turned off by a signal from a control device (not shown), so that the time constant of the differentiating circuit becomes small. Next, the same control signal as that in the above embodiment as shown in FIG. When the control signal changes from the "H" level to the "L" level, the transistors 11 and 13 are turned on and the transistor 16 is turned off, so that a current flows through the inductor 12. Further, as in the above-described embodiment, the capacitance variable circuit 19 is charged from the emitter of the transistor 11 through the base, but the time constant of the differentiating circuit is much smaller than that of the above-described embodiment, so that FIG. As shown in (b), the voltage at the output end of the capacitance variable circuit 19 rises sharply as compared with the above embodiment, and the threshold value (2.5 V) of the inverter 21 is instantaneously exceeded. Therefore, as shown in FIG. 3C, the time during which the "H" level voltage is applied to the base of the transistor 13, that is, the time during which the transistor 13 is in the ON state is extremely short as compared with the above embodiment. Therefore, the current flow of the inductor 12 is interrupted before the current sufficiently flows in the inductor 12 (before the saturation), and the counter electromotive force is generated in the inductor 12. Therefore, the counter electromotive force generated in the inductor 12 is as shown in FIG.
As shown in, the power supply voltage is reduced to about twice (about 10 V). As a result, the vibration of the piezoelectric buzzer 15 is weakened and the buzzer sound is reduced. Further, as shown in FIG. 3E, the vibration cycle of the piezoelectric buzzer 15 also has a pulse waveform with a duty ratio of about 50%, which is larger than that of the embodiment shown in FIG. 2E. As a result, the sound quality of the piezoelectric buzzer 15 becomes mellow than that with less harmonic components. As described above, according to the present embodiment, by changing the time constant of the differentiating circuit by the capacitance varying circuit 19, the volume and sound quality of the piezoelectric buzzer 15 can be easily switched.

[0014]

Since the present invention is configured as described above, it has the following effects. That is, since the time for energizing the inductor by the switching means can be optimized, useless saturation current flowing in the counter electromotive force generating means can be suppressed, and power consumption can be saved. . Also,
Since the voltage applied to the piezoelectric buzzer is a clean rectangular wave with no vibration, the buzzer sound of the piezoelectric buzzer is also a clear buzzer sound that does not include unnecessary harmonics.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a piezoelectric buzzer driving device of the present invention.

FIG. 2 is an operation waveform diagram in the apparatus of FIG.

FIG. 3 is another operation waveform diagram in the apparatus of FIG.

FIG. 4 is a circuit of a conventional piezoelectric audio output device.

5 is an operation waveform diagram in the circuit of FIG.

[Explanation of symbols]

 10 power supply 11, 13, 16 transistor 12 inductor 14 diode 15 piezoelectric buzzer

Claims (4)

[Claims] 1. A power source, an inductor for generating a counter electromotive force connected to the power source, and a first for generating a counter electromotive force in the inductor by controlling an energization time of a current from the power source to the inductor. No. 1 switching means, a piezoelectric buzzer connected to one end of the inductor, and a backflow prevention means disposed between the piezoelectric buzzer and the inductor and energizing the counter electromotive force generated in the inductor only in the piezoelectric buzzer direction. And a second for discharging the voltage applied to the piezoelectric buzzer and held by the backflow prevention means after a predetermined time.
2. A piezoelectric buzzer drive device, comprising: the switching means and the control means for controlling ON / OFF of the first switching means and the second switching means. 2. The first switching means comprises a first transistor arranged between the power source and the inductor, and a second transistor arranged between the inductor and the ground. The piezoelectric buzzer drive device according to claim 1. 3. The piezoelectric buzzer drive device according to claim 1, further comprising energization time varying means for varying on / off timing between the first switching means and the control device. . 4. The energization time varying means controls a connection / disconnection between a first capacitor, a second capacitor arranged in parallel with the first capacitor, and the second capacitor. The piezoelectric buzzer drive device according to claim 3, wherein the piezoelectric buzzer drive device is a differentiating circuit including a contacting / separating means and a resistor.